1. Field of the Invention
The present invention relates to a photoreactive resin composition used for forming various patterns on a surface of a substrate or inside the substrate, and to methods of manufacturing a circuit board and a ceramic multilayer substrate using the photoreactive resin composition.
2. Description of the Related Art
In recent years, radio-frequency electronic parts used for mobile communication equipment, satellite receivers, computers, and the like have been strongly required to have a small size and high performance. Also, wiring patterns of radio-frequency electronic parts have been required to comply with a higher density and higher-speed signals. In order to achieve a higher density and higher-speed signals, it is necessary to make wiring patterns fine and thick and make via holes fine.
In a radio-frequency electronic part, wiring patterns and via holes are conventionally formed by a screen printing process. Namely, a wiring pattern is formed by printing, through a predetermined screen mask, conductor paste formed by mixing a conductive metal powder and an organic vehicle comprising an organic binder and an organic solvent, and then baking the coated paste. A via hole is formed by printing, through a predetermined screen mask, insulator paste formed by mixing an insulating inorganic powder such as glass or the like and an organic vehicle, filling a hole formed for a via hole with conductor paste, and then baking the paste.
However, the above-described screen printing process has a problem in which refining of wiring patterns and via holes cannot be sufficiently achieved due to blurring and thinning. Particularly, in forming a wiring pattern by the screen printing process, the edge of the pattern is made thinner than the central portion of the pattern due to sagging during leveling. At a radio frequency, the so-called edge effect of concentrating a current at the edge of the pattern is significant, and thus the thinned edge of the pattern has the problem of causing disadvantages to speeding up signals at a radio frequency.
Therefore, a photolithography process using a photoreactive resin composition is proposed in Japanese Unexamined Patent Application Publication No. 1-296534. This process comprises coating, on a substrate, a photoreactive resin composition containing an inorganic powder (a conductive metal power for forming wiring patterns, or a glass power for forming an insulating layer having via hole holes) and a photoreactive organic component comprising an alkali-soluble polymer, a monomer having an ethylenically unsaturated double bond, and a photoreaction initiator; forming a mask in contact with the coated film after drying; patterning the film by exposure and development with an alkali developer; and then burning the patterned film to form a wiring pattern in a predetermined shape or an insulating layer having via-hole holes.
This method uses the photolithography process and is thus capable of forming fine and thick wiring patterns and an insulating layer having fine via holes, as compared with the screen printing process. This method is also capable of forming a pattern having a central portion and an edge portion which have substantially the same thickness. Therefore, this method can obtain wiring patterns and via holes advantageous in increasing the density and signal speed at radio frequencies, as compared with the screen printing process.
However, the photoreactive resin composition has low exposure sensitivity, and thus has the problem of low resolution of pattern formation.
Therefore, Japanese Unexamined Patent Application Publication No. 2000-204130 proposes a method of using an ethylenically unsaturated alkali-soluble polymer. This method can increase the exposure sensitivity of a photoreactive resin composition, thereby obtaining a high-resolution pattern.
However, when an inorganic powder containing a polyvalent metal power of copper or the like or a polyvalent metal oxide powder of boron oxide or the like is used for a photoreactive resin composition comprising an alkali-soluble polymer containing an ethylenically unsaturated double bond, the problem of gelling the photoreactive resin composition occurs.
As a means for preventing gelation of the photoreactive resin composition, Japanese Unexamined Patent Application Publication No. 3-205462 discloses that benzotriazole or the like is added as a stabilizer. This means cannot sufficiently prevent gelation for the following reason.
The photoreactive resin composition basically has the property of being readily gelled due to the reaction of acid functional groups (carboxyl groups and the like) in the alkali-soluble polymer with a polyvalent metal hydroxide on the surfaces of the inorganic powder containing the polyvalent metal power or polyvalent metal oxide powder. However, the stabilizer such as benzotriazole can slow down the reaction of the acid functional groups with the polyvalent metal hydroxide. When the ethylenically unsaturated double bond is added to the alkali-soluble polymer in order to improve the sensitivity of the photoreactive resin composition, the ethylenically unsaturated double bond acts on the polyvalent metal hydroxide to accelerate the reaction of the acid functional groups in the alkali-soluble polymer with the polyvalent metal hydroxide. Thus, the stabilizer cannot slow down the reaction of the acid function groups in the alkali-soluble polymer with the polyvalent metal hydroxide, thereby failing to prevent gelation.
Gelation of the photoreactive resin composition causes difficulty in coating and destabilizes the development process even if coating is possible.
Accordingly, it is an object of the present invention to provide a photoreactive resin composition having high exposure sensitivity and causing no gelation. Another object of the present invention is to provide methods of manufacturing a circuit board and a ceramic multilayer substrate each having wiring patterns and via holes formed by the photolithography process using the photoreactive resin composition.
As a result of intensive research for solving the above problem, the inventors found that by adding a predetermined amount of polymer having a pyrrolidone ring in a side chain to a photoreactive resin composition comprising an alkali-soluble polymer having an ethylenically unsaturated double bond, gelation of the photoreactive resin composition can be effectively prevented while maintaining high sensitivity.
Namely, the present invention relates to a photoreactive resin composition comprising (a) an inorganic powder containing a polyvalent metal powder and/or a polyvalent metal oxide powder, (b) an alkali-soluble first polymer having an ethylenically unsaturated double bond, (c) a monomer having an ethylenically unsaturated double bond, (d) a photoreaction initiator, (e) an organic solvent, and (f) a second polymer having a pyrrolidone ring in a side chain.
Particularly, the photoreactive resin composition of the present invention contains the second polymer having a pyrrolidone ring in a side chain, and the reaction of the acid functional groups in the alkali-soluble first polymer with the polyvalent metal hydroxide on the surfaces of the inorganic powder containing the polyvalent metal powder and/or the polyvalent metal oxide powder can be significantly slowed down even when the first polymer has the ethylenically unsaturated double bond, thereby preventing gelation of the photoreactive resin composition.
This is because a micro gel produced by the reaction of the second polymer having a pyrrolidone ring in a side chain with the polyvalent metal hydroxide causes steric hindrance to inhibit the action of the ethylenically unsaturated double bond in the alkali-soluble first polymer on the polyvalent metal hydroxide, significantly slowing down the reaction of the acid functional groups of the first polymer with the polyvalent metal hydroxide.
In the photoreactive resin composition of the present invention, the polyvalent metal powder contained in the inorganic powder can be a copper powder, and the copper powder is preferably coated with a copper oxide. In this case, the oxygen content of the copper powder is preferably 0.4% by weight to 1.2% by weight.
In the photoreactive resin composition of the present invention, the second polymer is preferably a copolymer of vinylpyrrolidone and a monomer having an ethylenically unsaturated double bond. Alternatively, the second polymer may be a homopolymer. In this case, the second polymer is preferably polyvinylpyrrolidone.
In the photoreactive resin composition of the present invention, the Fikentscher viscosity characteristic value of the second polymer is preferably 15 to 60.
In the photoreactive resin composition of the present invention, the content of the second polymer is preferably 0.1 part by weight to 5 parts by weight based on 100 parts by weight of the polyvalent metal powder contained in the inorganic powder or 0.01 part by weight to 1 part by weight based on 100 parts by weight of the polyvalent metal oxide powder contained in the inorganic powder.
In the photoreactive resin composition of the present invention, the organic solvent preferably contains a diol compound having two hydroxyl groups per molecule.
The content of the organic solvent is preferably 10 times by weight to 50 times by weight larger than the second polymer.
The photoreactive resin composition of the present invention preferably further contains a polyhydric alcohol having four or more hydroxyl groups per molecule.
The present invention also provides a method of manufacturing a circuit board comprising the steps of coating the photoreactive resin composition of the present invention on a substrate, exposing and developing the photoreactive resin composition to form a predetermined pattern on the substrate, and baking the pattern.
The present invention also provides a method of manufacturing a circuit board comprising the steps of coating the photoreactive resin composition of the present invention on a supporting member, exposing and developing the photoreactive resin composition to form a predetermined pattern on the supporting member, transferring the pattern formed on the supporting member to a substrate, and baking the pattern.
Furthermore, the present invention provides a method of manufacturing a ceramic multilayer substrate comprising the steps of coating the photoreactive resin composition of the present invention on a ceramic green sheet, exposing and developing the photoreactive resin composition to form a predetermined pattern on the ceramic green sheet, laminating a plurality of the green sheets each having the pattern formed thereon to form a laminate, and baking the laminate.
Furthermore, the present invention provides a method of manufacturing a ceramic multilayer substrate comprising the steps of coating the photoreactive resin composition of the present invention on a supporting member, exposing and developing the photoreactive resin composition to form a predetermined pattern on the supporting member, transferring the pattern formed on the supporting member to a ceramic green sheet, laminating a plurality of the ceramic green sheets each having the pattern formed thereon to form a laminate, and baking the laminate.